Semiconductor metal oxide based gas sensor activated at zero heater power

Abstract

A gas sensor is formed by a thin-film semiconductor metal-oxide gas sensing layer, with a thermally conductive and electrically-insulating layer in direct physical contact with a back of the gas sensing layer to carry the gas sensing layer. Sensing circuitry applies a voltage to the gas sensing layer and measures a current flowing through the gas sensing layer. The current flowing through the gas sensing layer is indicative of whether a gas under detection has been detected by the gas sensing layer, and serves to self-heat the gas sensing layer. A support structure extends from a substrate to make direct physical contact with and carry the thermally conductive and electrically insulating layer about a perimeter of a back face thereof, with the support structure shaped to form an air gap between the back of the thermally conductive and electrically insulating layer and a front of the substrate.

1 . A gas sensor, comprising:
 a gas sensing layer made of a thin-film semiconductor metal oxide material;   a thermally conductive and electrically insulating layer in direct physical contact with a back side of the gas sensing layer to thereby support the gas sensing layer;   sensing circuitry configured to apply a voltage to the gas sensing layer and measure a resulting current flowing through the gas sensing layer;   wherein the current flowing through the gas sensing layer is indicative of whether a gas under detection has been detected by the gas sensing layer, and serves to self-heat the gas sensing layer; and   a support structure making direct physical contact with and carrying the thermally conductive and electrically insulating layer about a perimeter of a back face thereof, with the support structure being shaped such that an air gap is formed between the back face of the thermally conductive and electrically insulating layer and the support structure to thereby trap air and heat generated by the gas sensing layer from being radiated other than to the thermally conductive and electrically insulating layer.   
     
     
         2 . The gas sensor of  claim 1 , wherein an electrical conductance of the gas sensing layer increases in the presence of the gas under detection and decreases in the absence of the gas under detection. 
     
     
         3 . The gas sensor of  claim 1 , wherein the thin-film semiconductor metal oxide material comprises at least one of tin(IV)-oxide (SnO 2 ), tungsten(III)-oxide (W 2 O 3 ), and zinc oxide (ZnO). 
     
     
         4 . The gas sensor of  claim 1 , wherein the thin-film semiconductor metal oxide material includes a dopant. 
     
     
         5 . The gas sensor of  claim 4 , wherein the dopant comprises at least one of platinum and palladium. 
     
     
         6 . The gas sensor of  claim 1 , wherein the gas sensing layer has a thickness of between 50 nm and 60 nm. 
     
     
         7 . The gas sensor of  claim 1 , further comprising a substrate from which the support structure extends, and wherein the air gap is formed between the back face of the thermally conductive, insulating layer and a front face of the substrate. 
     
     
         8 . A method, comprising:
 applying a voltage to a gas sensing layer carried by a thermally conductive and electrically insulating layer that itself is carried by a support structure;   self-heating the gas sensing layer using current flowing through the gas sensing layer as a result of the applied voltage, also resulting in heating of air within an air gap defined between the support structure and the thermally conductive and electrically insulating layer; and   detecting a gas under detection by measuring the current flowing through the gas sensing layer, with an increase in the current indicating presence of the gas under detection and a decrease in the current indicating an absence of the gas under detection.   
     
     
         9 . The method of  claim 8 , further comprising forming the gas sensing layer from a thin-film semiconductor metal oxide material. 
     
     
         10 . The method of  claim 9 , wherein the thin-film semiconductor metal oxide material comprises at least one of tin(IV)-oxide (SnO 2 ), tungsten(III)-oxide (W 2 O 3 ), and zinc oxide (ZnO). 
     
     
         11 . The method of  claim 9 , further comprising doping the thin-film semiconductor metal oxide material with a dopant. 
     
     
         12 . The method of  claim 11 , wherein the dopant comprises at least one of platinum, and palladium. 
     
     
         13 . The method of  claim 8 , wherein the gas sensing layer is formed to have a thickness of between 50 nm and 60 nm. 
     
     
         14 . A gas sensor, comprising:
 a gas sensing layer;   a thermally conductive and electrically insulating layer in direct physical contact with a back side of the gas sensing layer to thereby support the gas sensing layer;   sensing circuitry configured to determine whether a gas under detection has been detected by the gas sensing layer while causing self-heating of the gas sensing layer; and   a support structure carrying the thermally conductive and electrically insulating layer about a perimeter of a back face thereof, with the support structure being shaped such that an air gap is formed between the back face of the thermally conductive and electrically insulating layer and the support structure.   
     
     
         15 . The gas sensor of  claim 14 , wherein an electrical conductance of the gas sensing layer increases in the presence of the gas under detection and decreases in the absence of the gas under detection. 
     
     
         16 . The gas sensor of  claim 14 , wherein the gas sensing layer has a thickness of between 50 nm and 60 nm. 
     
     
         17 . The gas sensor of  claim 14 , further comprising a substrate from which the support structure extends, and wherein the air gap is formed between the back face of the thermally conductive, insulating layer and a front face of the substrate. 
     
     
         18 . The gas sensor of  claim 14 , wherein the gas sensing layer is constructed from a doped thin-film semiconductor metal oxide material. 
     
     
         19 . The gas sensor of clam  18 , wherein the doped thin-film semiconductor metal oxide material comprises at least one of tin(IV)-oxide (SnO 2 ), tungsten(III)-oxide (W 2 O 3 ), and zinc oxide (ZnO). 
     
     
         20 . The gas sensor of clam  18 , wherein the doped thin-film semiconductor metal oxide material is doped with at least one of platinum, and palladium.